Relationship between passage of typhoon and harmful dinoflagellate Cochlodinium polykrikoides bloom

Abstract

To better understand the effects of typhoon on harmful alga Cochlodinium polykrikoides, we investigated the C. polykirkoides population dynamics in relation to hydrographic conditions in Korean coastal waters before and after the passage of typhoon. In 2019, red tide of C. polykrikoides have occurred from August 23 to September 24. After typhoon Lingling passed through the Yellow Sea, C. polykrikoides population in offshore water was significantly accumulated to inshore area of Namhae Island with southerly wind on September 8. Similar to field observations of red tide, a the particle diffusion model simulations based on field data on September 4 showed that moving pattern of C. polykrikoides bloom patches have greatly influenced by wind-driven current with typhoon, particularly when diel vertical migration applied model. However, a red tide of C. polykrikoides disappeared immediately after the passage of typhoon Tapah on September 23, which was directly passed through the Korea/Tsushima Strait, resulting in whole water mixing in blooming area. Due to difference pattern of red tide behavior after the passage of these typhoons, we compared the wind properties and wave energy with wave height of two typhoons. As a result, although both typhoons had a strong wind over 15 m·s-1 , the wind direction was quite different, which may have a critical role in accumulating the C. polykrikoides population to the inshore area (i.e., Lingling) and in dispersing the population to offshore water (i.e., Tapah). In particular, the wave energy for generating turbulence in typhoon Tapah (753.6 k J·m-2 for 48h) was greatly higher than that of typhoon Lingling (441.7 k J·m-2 for 48h). Therefore, the results implies that typhoons have an important role in determining the accumulation and termination of C. polykrikoides red tide through the physical effects of wind direction and wave energy.